1. Field of the Invention
The present invention relates to removing pollutants from bodies of water. In particular, the invention relates to portable Sub-Surface Flow Constructed Wetlands systems for use in removing waterborne pollutants.
2. Description of the Related Art
Sub-Surface Flow Constructed Wetlands (SSFCW) have been used in the past to treat a variety of pollutants in water. In principle, these systems consist of a waterproof liner, pea gravel, and various emergent aquatic plants, such as the common cattail, reed, or bulrush. The large surface area of the gravel provides space for the development of a complex microbial community that is capable of transforming and/or removing a broad spectrum of waterborne pollutants, including organic and inorganically-bound nutrients, heavy metals, and organic compounds. These organic compounds include pesticides and gasoline-range and diesel-range organics. In both SSFCW and natural wetlands, there are distinct oxygenated (aerobic) and oxygen-free (anaerobic) zones that are inhabited by a consortia of bacteria that are adapted to thriving in each zone. The common bulrush (genus Schenoplectus) has a deep root system that transports oxygen from the upper portion of the plant to the finely dispersed root system. This helps to create several microclimates within a cubic meter that are aerobic and anaerobic. Under aerobic conditions pollutants are oxidized (the removal of electrons) by bacteria (e.g., the conversion of ammonium to nitrate). Under anaerobic conditions, bacteria facilitate the reduction (addition of electrons) of compounds (e.g., the conversion of nitrate to nitrogen gas). In particular, both sulfur and selenium have been shown to be reduced under anaerobic conditions by sulfate-reducing bacterial biofilms. Due to the large surface area of the sticky biofilm coating the pea gravel and root systems there is a two to three log (99%-99.9%) removal of pathogenic bacteria and viruses. The prior art SSFCW publications have dealt with bench and field-scale projects for the treatment of individual and mixed pollutants. A paper entitled—Treatability Assessment of Industrial Wastes by a Portable Wetland Unit by Davies et al. published in Advances in Water Pollution Control: Constructed Wetlands in Water Pollution Control described the use of a portable gravel-based SSFCW as an assessment tool to test the potential of a full-scale SSFCW. The unit (described by Davies et al.) was strictly a diagnostic tool to test-treat waters from industrial sites, and to analyze the feasibility of permanent—in the ground gravel-based SSFCWs. The size of the unit was approximately 1′×2′×6′ and since it was filled with gravel, it provided a limited ability to treat contaminants. The differences and distinctions of this invention are described in subsequent sections of this application.